The subject of this thesis is (1) the description of the conducting properties of layered
high-temperature superconductors along the least conducting direction (perpendicular to
the planes) and (2) the frequency dependence of the noise and conductance of one- and
two-dimensional conductors. Both topics stress the potential importance of collective charge
fluctuations in low-dimensional conductors.
The thesis consists of two (almost) independent parts. In the first part, a theoretical
model of conduction between the planes ( c-axis conduction) of layered high-temperature
superconductors in the normal state is presented. The main idea of the model is that tunneling
between planes is hindered by voltage fluctuations between the tunneling points. The
question of the conservation of electron momentum parallel to the planes during tunneling is
carefully examined. Various spectra of voltage fluctuations are evaluated in order to analyze
the applicability of the model. The temperature and frequency dependencies of the c-axis
conductivity are calculated from the premises of the proposed model. Experimental data are
summarized and analyzed in the framework of this model. The relevance of the proposed
model for other layered systems is discussed.
In the second part, the frequency dependence of conductance and Johnson-Nyquist noise
is calculated for one-dimensional wires and two-dimensional films. In low-dimensional conductors,
collective effects become important even at low frequencies and lead to the predicted
novel effects. Two different ways to derive the spectrum of charge fluctuations are demonstrated.
Certain frequency dependencies of noise and conductance for one-dimensional wires
and two-dimensional films, which can be subjected to experimental test, are predicted.